Misura della resistenza d`isolamento e della

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Misura della resistenza d`isolamento e della
Misura della resistenza d'isolamento e della resistività volumica di un provino di
gomma per piastre sottorotaia.
La resistenza d'isolamento trasversale è indicata dalle norme CEI come il rapporto fra
la tensione continua applicata tra due elettrodi posti su due facce opposte di un provino
da esaminare e la corrente stazionaria fra i due elettrodi, escludendo la corrente che
circola in superficie e non tenendo conto dei fenomeni di eventuale polarizzazione sugli
elettrodi.
Se non diversamente specificato la resistenza trasversale è misurata dopo un minuto
dall’applicazione della tensione.
La resistività di volume è indicata come il rapporto tra l’intensità del campo elettrico e
la densità della corrente permanente in un materiale isolante. Praticamente corrisponde
alla resistenza trasversale riferita ad un cubo di volume unitario. Essa è espressa in
Ωxmetro o Ωxcm.
Il metodo utilizzato è il metodo voltamperometrico basato sulla misura simultanea della
tensione continua applicata al provino e della corrente che l’attraversa.
La precisione totale richiesta dalle norme CEI è ± 10%.
Per evitare errori di misura derivanti da correnti di dispersione superficiali si è adottato
un dispositivo di guardia che è compreso nella cella Keithley di misura adoperata,
secondo lo schema seguente.
SCHEMA
A
resistività volumica
STRUMENTAZIONE ADOPERATA
Alimentatore: Kepco BOP 100-1 M
0 ÷ 100 V
0 ÷ 1000 mA
Cella di misura: Keithley mod. 6105
Dimensioni degli elettrodi:
Diametro elettrodo interno d1 = 5,08 ± 0,01 cm
Diametro interno elettrodo esterno d2 = 5,72 ± 0,01 cm
Spazio interelettrodico g = 0,32 ± 0,01 cm
Voltmetro: multimetro Fluke 45
Portata: 100 V
Risoluzione: 1 mV
Amperometro: Keithley 2000
DATI DEL PROVINO IN ESAME:
Profilo in gomma EPDM (Ethylene Propylene Diene Monomer) per rotaie
Spessore medio h = 0,805 ± 0,001 cm
Appendices
Specifications
A
Maximum Input
1000V dc or peak ac on any range
45
Users Manual
DC Voltage
Range
Resolution
Slow
True RMS AC Voltage, AC-Coupled
Resolution
Range
Slow
Medium
Fast
Accuracy
Medium
Fast
(6 Months)
(1 Year)
100 µV
002 % + 2
0.025 % + 2
100 µV
1 mV
0.02 % + 2
0.025 % + 2
1 mV
10 mV
0.02 % + 2
0.025 % + 2
300 mV
—
10 µV
3V
—
30 V
—
300 mV
—
10 µV
100 µV
300 V
—
10 mV
100 mV
0.02 % + 2
0.025 % + 2
3V
—
100µV
1 mV
1000 V
—
100 mV
1V
0.02 % + 2
0.025 % + 2
30 V
—
1 mV
10 mV
300 V
—
10 mV
100 mV
750 V
—
100 mV
1V
100 mV
1 µV
—
—
1000 mV
10 µV
—
—
10 V
100 µV
—
—
100 V
1 mV
—
—
750 V
10 mV
—
—
100 mV
1 µV
—
—
0.02 % + 6
0.025 % + 6
1000 mV
10 µV
—
—
0.02 % + 6
0.025 % + 6
10 V
100 µV
—
—
0.02 % + 6
0.025 % + 6
100 V
1 mV
—
—
0.02 % + 6
0.025 % + 6
1000 V
10 mV
—
—
0.02 % + 6
0.025 % + 6
Input Impedance
10 Me in parallel with <100 pF
Note
In the dual display mode, when the volts ac and volts dc functions are
selected, the 10 MΩ dc input divider is in parallel with the 1 MΩ ac
divider.
Accuracy
Linear Accuracy
dB Accuracy
Frequency
Power*
Slow/Med
Fast
Max
Input at
Upper
Freq
Slow
Medium
Fast
20-50 Hz
1 % + 100
1 % + 10
7%+2
0.15
0.72
2 % + 10
750 V
50 Hz-10 kHz
0.2 % + 100
0.2 % + 10
0.5 % + 2
0.08
0.17
0.4 % + 10
750 V
10-20 kHz
0.5 % + 100
0.5 % + 10
0.5 % + 2
0.11
0.17
1 % + 10
750 V
20-50 kHz
2 % + 200
2 % + 20
2%+3
0.29
0.34
4 % + 20
400 V
50-100 kHz
5 % + 500
5 % + 50
5%+6
0.70
0.78
10 % + 50
200 V
Normal Mode Rejection Ratio
>80 dB at 50 Hz or 60 Hz, slow and medium rates
>54 dB for frequencies between 50-440 Hz, slow and medium rates
>60 dB at 50 Hz, fast rate (Note: Fast rate has no filtering)
Maximum Allowable AC Voltage While Measuring DC Voltage or (AC + DC)
Voltages
* Error in power mode will not exceed twice the linear accuracy specification
Range
Max Allowable Peak AC
Voltage
Accuracy specifications apply within the following limits, based on reading rate:
Slow Reading Rate: Between 15,000 and 99,999 counts (full range)
Medium Reading Rate: Between 1,500 and 30,000 counts (full range)
Fast Reading Rate: Between 150 and 3,000 counts (full range)
Decibel Resolution
Resolution
Slow & Medium
0.01 dB
Peak Normal Mode Signal
NMRR* >80 dB†
100 mV
15 V
15 V
15 V
3V
1000 mV
15 V
15 V
15 V
30 V
10 V
1000 V
50 V
300 V
300 V
100 V
1000 V
50 V
300 V
1000 V
1000 V
1000 V
200 V
1000 V
* NMRR is the Normal Mode Rejection Ratio
† Normal Mode Rejection Ratio at 50 Hz or 60 Hz ±0.1 %
Fast
0.1 dB
Common Mode Rejection Ratio
>90 dB at do, 50 or 60 Hz, (1 ke unbalanced, medium and slow rates)
A-3
NMRR >60 dB†
300 mV
2000 6½-Digit Multimeter Specifications
2000 6½-Digit Multimeter Specifications
TRUE RMS AC VOLTAGE AND CURRENT CHARACTERISTICS
DC CHARACTERISTICS
CONDITIONS:
Function
Voltage
Resistance15
MED (1 PLC)1 or SLOW (10 PLC)
or MED (1 PLC) with filter of 10
Range
Resolution
Ω
Ω
Ω
Ω
16
Ω
11, 16
Ω
11, 16
Current
Ω
Ω
Ω
Ω
Ω
Test Current Or
Burden Voltage
(±5%)
Ω
Ω
Ω
Ω
Ω
Continuity 2W
Diode Test
ACCURACY: ±(ppm of reading + ppm of range)
(ppm = parts per million) (e.g., 10ppm = 0.001%)
Input
Resistance
24 Hour14
23°C ±1°
Ω
Ω
Ω
ΜΩ ±1%
Ω ±1%
Ω
Ω
90 Day
23°C ±5°
1 Year
23°C ±5°
Temperature
Coefficient
0°-18°C &
28°-50°C
ACCURACY1: ±(% of reading + % of range), 23°C ±5 °C
Voltage Range
Resolution
Current Range
Resolution
Calibration Cycle
3 Hz-10 Hz
#
$
!"
Temperature
Coefficient/°C8
Calibration Cycle
3 Hz-10 Hz
!#
$
!#
$
Temperature
Coefficient/°C8
High Crest Factor Additional Error ±(% of reading)7
CREST FACTOR:
ADDITIONAL ERROR:
%
%
%
%
AC Operating Characteristics2
Function
Digits
Readings/s
&
&
&
&
&
3
4 55$ )
"67
'38
4 55$ )
"6
"$
'()
Rate
*+,
1*2
1*2
0
0
0
0
0
MED
SLOW
./
./
./
./
./
./
10 Hz-20 kHz
20 kHz-50 kHz 50 kHz-100 kHz 100 kHz-300 kHz
10 Hz-5 kHz
AC System Speeds2, 5
FUNCTION/RANGE CHANGE6: "
AUTORANGE TIME:"
ASCII READINGS TO RS-232 (19.2k BAUD)4:"
MAX. INTERNAL TRIGGER RATE4:"
MAX. EXTERNAL TRIGGER RATE4:"
Bandwidth
./0./
./0./
./0./
./0./
./0./
Additional Low Frequency Errors ±(% of reading)
./
./
./
./
./
FAST
9
9
AC General
INPUT IMPEDANCE: Ω:;< $ 55
5
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ACV INPUT PROTECTION: <
MAXIMUM DCV: > !3$ )
ACI INPUT PROTECTION: [email protected]"
BURDEN VOLTAGE: )
A$" )
A$"
SHUNT RESISTOR: Ω> 5538$ )
"
AC CMRR: 'BC(DEΩ(+,5
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MAXIMUM CREST FACTOR: [email protected]"F 5
VOLT HERTZ PRODUCT: GH./
OVERRANGE: ;>?$ )
IF
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AC Notes
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SECTION 2.
2-1.
~th
PREPARATION FOR U5E.
The Model 6105 1s shipped
b. Surface Resistivity Measurements. Place the
short circuit plug aver the lower two jacks, 1eaving
"SURFACE" clearly visible. Insert the banana plug
from the test weight assembly into the top jack. Clese
the Model 6105 cover. Apply the power supply voltage. Read the current 00 the electrometer. The value
of tbe surface resistivity ls found through the following calculation:
two thumb-screw fasteners holding the test weight
to the guard ring. Remove these fasteners and stare
far later use. These are used only far shipp1ng and
they should nct be used during measurements. In
mounting the sample far measurement, make sure there
are no conductive paths between the electrodes other
than thase through the sample. The sample should be
supported trom the electrodes so tbat the electrodes
do Dct touch anything excep.t the sample. Do not handle
the sample with bare fingers; acetate rayon gloves are
recommended. Far best results, clean tbe sample surfaces with an alcaho! and ether mixture or' other suitable solvent.
a. Volume Resistivity Measurements. PIace the
ahart circuit plug over the upper two jacks, leaving
"VOLUME" clearly visible. Insert the banana plug from
the test weight assembly into the bottoro jack. Close
the Mode1 6105 cover. An inter10ck switch disconnects
the potential to the sample if the cover 1s opened.
Apply the power supply voltage. Read the current on
the e1eetrometer. The value of the volume resistivity
p, 1s found through one cf the f01lowing calculations:
p
te I
53.4 V
--1--
ohms
where o is the surface resistivity of the sample;
v is the applied vo1tage from the power supply
in valts;
I is the current reading from che electrometer.
2-2. CONNECTIONS~ Connect the power supply to the
uhf-type receptacle. Connect the eleetrometer to the
bnc-type receptacle. PIace the sample under the test
weight as shown in Figure 5. !be sample thickness
should be between 1/16 and 1/4 inch (0.159 and 0.635
cm). The diameter should be berween 2-1/2 and 4 inches
(6.29 and 10.2 cm).
ehm-centimeters
is the volume resistivity of the sample;
V is the applied voltage from the power supply
in volts;
ti is the average thickness cf the sample in
inehes;
te is the average thickuess cf the sample in
centimeters;
l is the current reading fram the eleetrometer.
2-3. PROCEDURE. The Model 6105 permits easy measurement of a sample. Thc test sample is placed betweeo
the two electrodes; the dcsired test potential 15
selected from the voltage supply and the current passing through tbe test sample is measured by the electrometer. From readings from the voltage supply and
the electrometer. the resistivities can be computed.
t
2 in.
2-1/8 in.
5.40 cm.
5.08 cm.
(Do)
3-1/4 in.
2-1/4 in.
5.72
1/8 in .
. 31 cm.
FIGURE 3.
2
~
3.53 V ohm-inches
22.9 V
p
a
"'ti!
p = ------
where
OPERATION
DIMENSIONING FOR MODEL 6105 ELECTRODES
C1U.
8.25 cm.